1. Field of the Invention
The present invention relates to an endoscope system that irradiates the inside of a body cavity with light from a plurality of semiconductor light sources such as LEDs, and an operating method of the endoscope system.
2. Description Related to the Prior Art
In medical service, diagnosis and treatment using an endoscope system, having a light source apparatus, an endoscope, and a processing apparatus, have become widespread. As the light source apparatus of the endoscope system, a broadband light source such as a xenon lamp has been widely used, and furthermore, a semiconductor light source including an LED (light emitting diode), an LD (laser diode), and the like are becoming available.
It is known that a light amount of the semiconductor light source varies with temperature variation, aging degradation, and the like. In the case of using a combination of a plurality of color semiconductor light sources, the ratio in the emitted light amount between the plural color semiconductor light sources is necessarily set at a predetermined value even at any brightness. However, variation in the emitted light amount of any color of the semiconductor light sources due to the temperature variation or the like makes the ratio go out of the set value to create a change in a color tone.
For this reason, according to Japanese Patent Laid-Open Publication No. 2010-158413, in order to prevent variation in the light amount, a light receiver such as a sensor detects the light amount, and the operation of the semiconductor light sources is controlled based on the detection result, such that color temperature of emission light is made constant. According to Japanese Patent No. 4787032, in order to prevent variation in the light amount, a temperature sensor detects the temperature of the semiconductor light source, and a processing apparatus changes a gain by which an image signal is multiplied in accordance with the detection result of the temperature sensor. Changing the gain prevents variation in the image signal caused by variation in the light amount. However, Japanese Patent No. 4787032 cannot detect the aging degradation.
It is known that a temperature drift (wavelength shift) occurs in the semiconductor light source in accordance with a current value applied to the semiconductor light source, in other words, light intensity, in addition to the variation in the emitted light amount as described above. In the case of the R-LED, as illustrated in FIG. 18, a peak wavelength shifts to a long wavelength side with an increase in the light intensity (“low”, “medium” and “high” represent the magnitude of the light intensity in FIG. 18 and also FIG. 20). The wavelength shift changes a color tone of an endoscopic image, and hence variously affects imaging quality.
For example, in imaging using a dye e.g. crystal violet, as illustrated in FIG. 19, an output value (reflected light amount) of the crystal violet goes out of linear proportion at a high level of the light intensity of the R-LED. Especially, redness becomes strong as the emitted light amount of the R-LED increases, just as in the case of telephoto imaging. This is because, as illustrated in FIG. 20, in addition to that the peak wavelength of the R-LED shifts to the long wavelength side with an increase in the light intensity, the reflectivity of the crystal violet gradually increases on the longer wavelength side than 600 nm, and therefore, the reflected light amount of the R-LED becomes too large. The strong redness at a portion having the crystal violet due to the wavelength shift may cause a doctor to confuse the crystal violet with bleeding tissue.
The change in the color tone e.g. a change of color of the crystal violet associated with the wavelength shift, as described above, needs correcting in accordance with the wavelength shift. Neither the light source correction as described in Japanese Patent Laid-Open Publication No. 2010-158413 nor the gain modification as described in Japanese Patent No. 4787032 is adequate for such a correction.